You assign a practitioner to a location by clicking on the 'Locations' section in their record. This then brings up the locations they are assigned to (if any).
When the locations load, simply click 'Add another location.'
Then you will be prompted choose another location from the dropdown:
Once selected, the additional location it will appear under 'Locations' in the record.
You can also select whether the practitioner will use different charges depending on which location they are at. If you select 'Use different charges at different locations' it will show the charges for each location separately.